In a conventional manual transmission, a mechanical linkage is provided between the gearshift lever and the one or more shift rods of the transmission. By moving the shift lever into a selected gear position, the linkage can move one of the shift rods in the transmission, thereby selecting the appropriate gear in the gearbox. Automated manual transmissions have been introduced in order to remove the need for the mechanical linkage between the shift lever and shift rods. In place of the mechanical linkage, hydraulic pistons may be provided at either end of each shift rod. Each shift rod may also provided with solenoid shift rod valves at either end thereof to control hydraulic pressure on the pistons.
When in neutral, the hydraulic pressure at either end of the shift rod balances the rod in the centered, neutral position. Once the position of the gear lever indicates the desired gear, one of the solenoid shift rod valves will be instructed to release the fluid at one end of the shift rod. The rod will then move under the hydraulic pressure at the opposite end in order to engage the desired gear. An example of such a system is disclosed in U.S. Pat. No. 6,301,984 to Petzold, which also includes position sensors that are used to ensure that the hydraulic pistons to not strike stop surfaces after the desired gear is selected.
As in a conventional manual transmission, automated manual transmissions still retain synchronizers to assist in the engagement of the selected gear. However, even with automated manual transmissions provided with synchronizers, the engagement of the shift collar with the selected gear is often abrupt, as it is controlled by an electronic controller rather than by the feel of the vehicle operator. This abrupt engagement of the gear can make it difficult for an operator to operate a vehicle smoothly, thereby increasing operator fatigue. Furthermore, the abrupt engagement also means that the power transmission efficiency of automated manual transmissions is not as great as that obtained with conventional manual transmissions.
It is an aim of the present invention to solve one or more of the problems set forth above.